An exemplary embodiment of this application relates to a multicolor development system for an electrophotographic reproducing machine. More particularly, the exemplary embodiment relates to a multicolor development system having a plurality of non-interactive development apparatus, each of which generate a respective toner cloud adjacent the machine's photoreceptor as the photoreceptor is moved past each of the development apparatuses. The toner clouds develop and render visible successive portions of a multicolor latent electrostatic image on the photoreceptor with substantially no scavenging or redevelopment of a first developed image portion.
One type of electrophotographic reproducing machine is a xerographic copier or printer. In a typical xerographic copier or printer, a photoreceptor surface is generally arranged to move in an endless path through the various processing stations of the xerographic process. As in most xerographic machines, a light image of an original document is projected or scanned onto a uniformly charged surface of a photoreceptor to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged powdered developing material called toner to form a toner image corresponding to the latent image on the photoreceptor surface. When the photoreceptor surface is reusable, the toner image is then electrostatically transferred to a recording medium, such as paper, and the surface of the photoreceptor is prepared to be used once again for the reproduction of a copy of an original. The paper with the powdered toner thereon in imagewise configuration is separated from the photoreceptor and moved through a fuser to permanently fix or fuse the toner image to the paper.
Development of full color or multicolor electrostatic latent images requires non-interactive development systems to prevent the disturbance and contamination of previously developed image portions. Generally, full color electrostatic latent images are generally composed of a set of scanned images serially superimposed on top of each other. Each of the scanned images represent one color of the multicolor original document, and hence such multicolor latent image is often referred to as image-on-image. Usually the magenta image portion of the latent image is developed first, followed by a yellow portion, then cyan, and finally black. Clearly, the first developed image must not be disturbed by the subsequently developed image nor must there be cross contamination of the toner images.
The type of development systems which do not disturb or cross contaminate the images as they are separately developed are referred to as non-interactive development devices and primarily relate to various powder cloud development systems. There are a number of well known non-interactive development systems, such as, for example, the scavengeless development devices as disclosed in U.S. Pat. Nos. 4,868,600 and 5,504,563. However, as the speed of the reproducing machines increase and the resolution of the images increase, the short comings of the existing non-interactive development devices become more pronounced. Some scavengeless development systems required stationary wire electrodes located in the toner clouds that become contaminated with toner, additives and other debris, while others types require expensive interdigitated electrodes on donor rolls addressed by a robust commutator.
Toner development systems normally fall into two catagories; viz., those that use carrier beads or granules and toner particles and those that use only toner particles for the developer material. The carrier beads are usually magnetic and the toner particles are usually nonmagnetic, but triboelectrically adhere to the carrier beads. The toner particles are attracted to the electrostatic latent image and form a toner particle image on the photoreceptor surface. As indicated above, the toner particle image is transferred from the surface of the photoreceptor to a recording medium, such as paper, and then the toner particle image is heated to fuse it permanently to the recording medium in image configuration.
Triboelectric charging of the toner particles is obtained by mixing the toner particles with the larger carrier beads in a two component developer material or by rubbing the toner particles between a doctor blade and a donor member in a single component developer material. Magnetic brush development systems generally have a sleeve that axially rotates with fixed internal magnets that attract magnetic carrier beads thereto from a sump and transport them to a development zone adjacent the movable photoreceptor. Non-magnetic particles of toner are triboelectrically attracted to the carrier beads, and as the toner particles, hereafter called toner, enters the development zone, the toner is attracted from the carrier beads to the electrostatic latent image on the confronting surface of the photoreceptor. Jumping development systems attract toner from a sump onto an axially rotated donor roll which rotates the toner to a location spaced from but adjacent a electrostatic latent image on a moving photoreceptor. The toner is attracted from the donor roll to the electrostatic latent image and jumped across the space or gap to render the electrostatic latent image visible. Such commercial development systems as magnetic brush or jumping single component development systems interact with the photoreceptor and a previously toned image will be scavenged by subsequent development.
There are many existing scavengeless development systems that prevent interaction of the development system with the previously developed image. For example, U.S. Pat. No. 4,868,600 discloses a scavengeless development system in which toner detachment from a donor roll and the concomitant generation of a toner cloud is obtained by AC electric fields supplied by spaced wire electrodes positioned in close proximity to the donor roll and within the space between the donor roll and the photoreceptor surface containing the electrostatic latent image. However, the wire electrodes are subject to contamination by toner and other debris that impacts the performance of the wire electrodes.
U.S. Pat. No. 5,276,488 discloses a scavengeless development system in which toner is detached from a donor belt and attracted to an electrostatic latent image carried by a moving photoreceptor positioned adjacent the belt. Generation of a toner cloud is effected using AC electric fields created by applying an AC voltage to an embedded interdigitated electrode structure in a shoe stationarily positioned behind the donor belt. One disadvantage of such a configuration is that the electric field at the toner layer on the donor belt is reduced by the thickness of the belt, so mechanically robust belts cannot be used. Furthermore, if interdigitated electrodes are used in the shoe, the dielectric polarization of the belt material will tend to shunt the electric field from the AC biased electrodes, and the electric field falls off exponentially with increasing belt thickness and decreasing spacing between the electrodes.
U.S. Pat. No. 5,504,563 discloses a scavengeless or non-interactive development system in which an AC bias is applied between neighboring interdigitated electrodes embedded in a rotating donor roll or belt. In addition to requiring high manufacturing tolerances, such interdigitated electrodes require a robust commutator device for supplying a high AC voltage thereto, so that the manufacturing costs are high.